1. Field of the Invention
The present invention relates to a stage apparatus for substantially linearly moving a movable stage, that supports an image pickup device (e.g., CCD image sensor), in two orthogonal directions on a plane, and a camera shake correction apparatus using such a stage apparatus.
2. Description of the Prior Art
A known stage apparatus used as a camera shake correction apparatus in which a movable stage is substantially linearly moved in two orthogonal directions in a plane is described in, for example, Japanese laid-open patent publication H6-46314.
Such a known stage apparatus (shake correction apparatus) is provided with a square frame member having an inside space in which an X-direction driving system (first drive system) and a Y-direction driving system (second drive system) are installed. The X-direction driving system is composed of a pair of Y-direction leaf springs (parallel leaf springs) which extend from an inner surface of one side of the square frame member (casing) in a specific Y-direction, and an X-direction movable movable member (first movable member) which extends in an X-direction orthogonal to the Y-direction to connect ends of the pair of Y-direction leaf springs to each other. The Y-direction driving system is composed of a fixing member which extends in the Y-direction from the X-direction movable member, a pair of X-direction leaf springs (parallel leaf springs) which extend from the fixing member in the X-direction, and a Y-direction movable member (second movable member) which extends in the Y-direction to connect ends of the pair of X-direction leaf springs to each other. An image pickup device is fixed to the Y-direction movable member.
The stage apparatus is provided between the square frame member and the X-direction movable member with an X-direction actuator which is composed of a square planar coil and a magnetic circuit for driving the X-direction movable member in the X-direction, and is provided between the X-direction movable member and the Y-direction movable member with a Y-direction actuator which is composed of a square planar coil and a magnetic circuit for driving the Y-direction movable member in the Y-direction.
Accordingly, applying a driving force on the X-direction movable member in the X-direction via the X-direction actuator causes the pair of Y-direction leaf springs to be resiliently deformed in the X-direction, and this resilient deformation of the pair of Y-direction leaf springs causes the X-direction movable member, the Y-direction movable member and the image pickup device to move linearly in the X-direction (substantially linearly in the X-direction with a slight displacement in the Y-direction in practice because the pair of Y-direction leaf springs are resiliently bent) to correct camera shake in the X-direction. On the other hand, giving the Y-direction movable member a driving force in the Y-direction via the Y-direction actuator causes the pair of X-direction leaf springs to be resiliently deformed in the Y-direction, and this resilient deformation of the pair of X-direction leaf springs causes the Y-direction movable member and the image pickup device to move linearly in the Y-direction (substantially linearly in the Y-direction with a slight displacement in the X-direction in practice because the pair of X-direction leaf springs are resiliently bent) to correct camera shake in the Y-direction.
It is troublesome to assemble the shake correction apparatus disclosed in the aforementioned Japanese laid-open patent publication (H6-46314) because the square frame member, the pair of Y-direction leaf springs, the pair of X-direction movable member, the fixing member, the pair of X-direction leaf springs and the Y-direction movable member need to be connected to one another by adhesive or by fitting to complete the shake correction apparatus. Therefore, a high production cost of such a conventional shake correction apparatus is inevitable.
Additionally, if the pair of Y-direction leaf springs are reduced in size in the optical axis direction for the purpose of miniaturizing the shake correction apparatus in the optical axis direction, the weight of the X-direction movable member is exerted on the pair of Y-direction leaf springs if the shake correction apparatus is orientated so that the optical axis extends vertically (upward/downward direction), and the influence of this weight may bend and twist the pair of Y-direction leaf springs. This bending and twisting tend to occur in a middle portion of each Y-direction leaf spring in the lengthwise direction thereof. Once such bending and twisting occur, the square frame member and the X-direction movable member are displaced from each other in the optical axis direction. Due to this displacement, the imaging surface of the image pickup device does not lie in a plane orthogonal to the optical axis.
This problem also arises in the pair of X-direction leaf springs in the case where the pair of X-direction leaf springs are reduced in size in the optical axis direction because the weight of the Y-direction movable member is exerted on the pair of X-direction leaf springs if the shake correction apparatus is orientated so that the optical axis extends vertically.
Moreover, if the aforementioned bending and twisting exceed the deformable limit of each leaf spring, plastic deformation occurs in the pair of X-direction leaf springs or the pair of Y-direction leaf springs. Such a plastic deformation lowers the accuracy of focusing down to an unrecoverable degree. Moreover, the possibility of each leaf spring (each X-direction leaf spring and each Y-direction leaf spring) being bent and twisted is increased if each leaf spring falls into a habit of bending.
Furthermore, even if the shake correction apparatus is not orientated so that the optical axis extends vertically, there is a possibility of such problems arising if an unintentional force in the optical axis direction, which may be caused by, e.g., an impact applied to the camera when the camera is accidentally dropped to the floor, is applied to the pair of X-direction leaf springs and/or the pair of Y-direction leaf springs.